Nitroxide-Containing Amphiphilic Random Terpolymers for Marine Antifouling and Fouling-Release Coatings

Two types of amphiphilic random terpolymers, poly(ethylene glycol methyl ether methacrylate)-ran-poly(2,2,6,6-tetramethylpiperidinyloxy methacrylate)-ran-poly(polydimethyl siloxane methacrylate) (PEGMEMA-r-PTMA-r-PDMSMA), were synthesized and evaluated for antifouling (AF) and fouling-release (FR) properties using diverse marine fouling organisms. In the first stage of production, the two respective precursor amine terpolymers containing (2,2,6,6-tetramethyl-4-piperidyl methacrylate) units (PEGMEMA-r-PTMPM-r-PDMSMA) were synthesized by atom transfer radical polymerization using various comonomer ratios and two initiators: alkyl halide and fluoroalkyl halide. In the second stage, these were selectively oxidized to introduce nitroxide radical functionalities. Finally, the terpolymers were incorporated into a PDMS host matrix to create coatings. AF and FR properties were examined using the alga Ulva linza, the barnacle Balanus improvisus, and the tubeworm Ficopomatus enigmaticus. The effects of comonomer ratios on surface properties and fouling assay results for each set of coatings are discussed in detail. There were marked differences in the effectiveness of these systems against the different fouling organisms. The terpolymers had distinct advantages over monopolymeric systems across the different organisms, and the nonfluorinated PEG and nitroxide combination was identified as the most effective formulation against B. improvisus and F. enigmaticus.

Effect of Sputtering Temperature on Fluorocarbon Films: Surface Nanostructure and Fluorine/Carbon Ratio

In this work, fluorocarbon film was deposited on silicon (P/100) substrate using polytetrafluoroethylene (PTFE) as target material at elevated sputtering temperature. Field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were employed to investigate the surface morphology as well as structural and chemical compositions of the deposited film. The surface energy, as well as the polar and dispersion components, were determined by water contact angle (WCA) measurement. The experimental results indicated that increasing sputtering temperature effectively led to higher deposition rate, surface roughness and WCA of the film. It was found that the elevated temperature contributed to increasing saturated components (e.g., C-F2 and C-F3) and decreasing unsaturated components (e.g., C-C and C-CF), thus enhancing the fluorine-to-carbon (F/C) ratio. The results are expected aid in tailoring the design of fluorocarbon films for physicochemical properties.

Hydrolyzable Additive-Based Silicone Elastomers: A New Approach for Antifouling Coatings

Fouling Release Coatings are marine antifouling coatings based on silicone elastomers. Contrary to commonly used biocide-based antifouling coatings, they do not release biocides into the marine environment, however, they suffer from poor antifouling efficacy during idle periods. To improve their antifouling performances in static conditions, various amounts of hydrolyzable polymers were incorporated within a silicone matrix. These hydrolyzable polymers were chosen for the well-known hydrolytic degradation mechanism of their main chain, e.g. poly(ε-caprolactone) (PCL), or of their ester pending groups, e.g. poly(bis(trimethylsilyloxy)methylsilyl methacrylate) (PMATM2). The degradation kinetics of such hydrolyzable silicone coatings were assessed by mass loss measurements during immersion in deionized water. Coatings containing PMATM2 exhibited a maximum mass loss after 12 weeks, whereas PCL-based coatings showed no significant mass loss after 24 weeks. Dynamic contact angle measurements revealed the modifications of the coatings surface chemistry with an amphiphilic behavior after water exposure. The attachment of macrofoulers on these coatings were evaluated by field tests in the Mediterranean Sea, demonstrating the short or long-term antifouling effect of these hydrolyzable polymers embedded in the silicone matrix. The settlement of A. amphitrite barnacles on the different coatings indicated inhospitable behaviors towards larval barnacles for coatings with at least 15 wt % of additives.

Significantly Reduced Secondary-Electron-Yield of Aluminum Sheet with Fluorocarbon Coating

In this work, the surface of Al sheet was coated with a fluorocarbon (FC) thin film by radio frequency (RF) sputtering of polytetrafluoroethylene (PTFE) to investigate the influence of dielectric coatings on the secondary electron yield (SEY) behavior of Al sheets. Atomic-force microscopy (AFM) and energy-dispersive spectroscopy (EDS) were employed to identify the surface topographies and elemental contents of the samples with FC coatings. Water contact angle (WCA) measurements were performed to characterize the surface tension as well as the polar and dispersion components of the samples’ surface. The secondary electron- mission (SEE) behavior of the samples was determined by measuring the SEY coefficients in an ultra-high vacuum chamber with three electron guns. The experimental results indicated that the longer sputtering time effectively led to the increase in coating thickness and a higher ratio of F/C, as well as the continued decrease of surface tension. A quite thin FC coating of about 11.3 nm on Al sheet resulted in the value of maximum SEY (δmax) dropping from 3.02 to 1.85. The further increase in coating thickness beneficially decreased δmax down to 1.60, however, at the cost of a ten-fold thicker coating (ca. 113 nm). It is found that increasing the coating thickness contributes to reducing SEY coefficients as well as suppressing SEE. The results are expected to guide the design of dielectric-coating for SEY reduction as well as multipactor suppression on Al.

The Dispersion Tolerance of Micro/Nano Particle in Polydimethylsiloxane and Its Influence on the Properties of Fouling Release Coatings Based on Polydimethylsiloxane

Particles can be used to improve the mechanical properties of fouling release coatings based on polydimethylsiloxane (PDMS). In this study, coatings were prepared by high speed stirring using seven types of particles, with different particle size from nanometer to micrometer. The influence of specific surface area of the particles on the dispersion tolerance was investigated. The results showed that the dispersion tolerance of particles in PDMS decreased with the increase in specific surface area of the particle, and for nano particles, the factor most affecting the dispersion tolerance was the specific surface area of agglomerate particle. Subsequently, the surface properties, mechanical properties, and biofilm adhesion assay of coatings were investigated. Results indicated that surface roughness increased with the increase of dispersion tolerance. Surface roughness of samples improved the hydrophobicity of samples, yet the polar chemical group of nano silica and fumed silica reduced the hydrophobicity of samples. Further, particles could enhance the mechanical properties of coating, especially nano particles. Compared to the coating without particle, biofilm adhesion performance of coating with particles decreased, which was determined by the increase of the elastic modulus and surface roughness of coatings.

Model Amphiphilic Block Copolymers with Tailored Molecular Weight and Composition in PDMS-Based Films to Limit Soft Biofouling

A set of controlled surface composition films was produced utilizing amphiphilic block copolymers dispersed in a cross-linked poly(dimethylsiloxane) network. These block copolymers contained oligo(ethylene glycol) (PEGMA) and fluoroalkyl (AF6) side chains in selected ratios and molecular weights to control surface chemistry including antifouling and fouling-release performance. Such properties were assessed by carrying out assays using two algae, the green macroalga Ulva linza (favors attachment to polar surfaces) and the unicellular diatom Navicula incerta (favors attachment to nonpolar surfaces). All films performed well against U. linza and exhibited high removal of attached sporelings (young plants) under an applied shear stress, with the lower molecular weight block copolymers being the best performing in the set. The composition ratios from 50:50 to 60:40 of the AF6/PEGMA side groups were shown to be more effective, with several films exhibiting spontaneous removal of the sporelings. The cells of N. incerta were also removed from several coating compositions. All films were characterized by surface techniques including captive bubble contact angle, atomic force microscopy, and near edge X-ray absorption fine structure spectroscopy to correlate surface chemistry and morphology with biological performance.

Copolymer films containing amphiphilic side chains of well-defined fluoroalkyl-segment length with biofouling-release potential

Novel methacrylate copolymers containing polysiloxane (SiMA) and mixed poly(ethyleneglycol)-perfluorohexyl side chains (MEF) were synthesised and dispersed as surface-active additives in crosslinked PDMS films.

Photopolymerized Network Polysiloxane Films with Dangling Hydrophilic/Hydrophobic Chains for the Biofouling Release of Invasive Marine Serpulid Ficopomatus enigmaticus

Novel photopolymerized network films based on a polysiloxane matrix containing varied amounts of polyoxyethylene (P3) or perfluorohexylethyl (F) dangling side chains were investigated. For films containing less than 10 wt % P3 and F, the wettability and elastic modulus were similar to those of the photopolymerized network matrix. However, angle-resolved X-ray photoelectron spectroscopy measurements proved that the surface of films with F dangling chains was highly enriched in fluorine depending on both the amount of P3 and F and their relative ratio in the films. The biological performance of the films was evaluated against a new widespread and invasive marine biofoulant, the serpulid Ficopomatus enigmaticus. The diatom Navicula salinicola was also assayed as a conventional model organism for comparison. Films richer in P3 better resisted the settlement and promoted the release of calcified tubeworms of F. enigmaticus.

Anti-fouling Coatings of Poly(dimethylsiloxane) Devices for Biological and Biomedical Applications

Fouling initiated by nonspecific protein adsorption is a great challenge in biomedical applications, including biosensors, bioanalytical devices, and implants. Poly(dimethylsiloxane) (PDMS), a popular material with many attractive properties for device fabrication in the biomedical field, suffers serious fouling problems from protein adsorption due to its hydrophobic nature, which limits the practical use of PDMS-based devices. Effort has been made to develop biocompatible materials for anti-fouling coatings of PDMS. In this review, typical nonfouling materials for PDMS coatings are introduced and the associated basic anti-fouling mechanisms, including the steric repulsion mechanism and the hydration layer mechanism, are described. Understanding the relationships between the characteristics of coating materials and the accompanying anti-fouling mechanisms is critical for preparing PDMS coatings with desirable anti-fouling properties.

Non-toxic, non-biocide-release antifouling coatings based on molecular structure design for marine applications

Antifouling (AF) coatings bring economic benefits but raise environmental and health concerns. Non-toxic, non-biocide-release AF strategies are reviewed according to “detachment of biofoulants” and “prevention of attachment” approaches. Chemical and physical aspects of AF mechanisms and new amphiphilic, superhydrophilic and topographic AF strategies are discussed.

A comparison between different fouling-release elastomer coatings containing surface-active polymers

Surface-active polymers derived from styrene monomers containing siloxane (S), fluoroalkyl (F) and/or ethoxylated (E) side chains were blended with an elastomer matrix, either poly(dimethyl siloxane) (PDMS) or poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS), and spray-coated on top of PDMS or SEBS preformed films. By contact angle and X-ray photoelectron spectroscopy measurements, it was found that the surface-active polymer preferentially populated the outermost layers of the coating, despite its low content in the blend. However, the self-segregation process and the response to the external environment strongly depended on both the chemistry of the polymer and the type of matrix used for the blend. Additionally, mechanical testing showed that the elastic modulus of SEBS-based coatings was one order of magnitude higher than that of the corresponding PDMS-based coatings. The coatings were subjected to laboratory bioassays with the marine alga Ulva linza. PDMS-based coatings had superior fouling-release properties compared to the SEBS-based coatings.

An ecotoxicological study on tin- and bismuth-catalysed PDMS based coatings containing a surface-active polymer

Novel films were prepared by condensation curing reaction of a poly(dimethyl siloxane) (PDMS) matrix with bismuth neodecanoate and dibutyltin diacetate catalysts. An ecotoxicological study was performed on the leachates of the coatings using the bacterium Vibrio fischeri, the unicellular alga Dunaliella tertiolecta, the crustacean Artemia salina and the fish Sparus aurata (larvae) as testing organisms. A copper-based self-polishing commercial paint was also tested as reference. The results showed that the tin-catalysed coatings and the copper paint were highly toxic against at least two of the four test organisms, whereas bismuth-catalysed coatings did not show any toxic effect. Moreover, the same biological assessment was also carried out on PDMS coatings containing a surface-active fluorinated polymer. The toxicity of the entire polymeric system resulted only from the tin catalyst used for the condensation curing reaction, as the bismuth catalysed coatings incorporating the surface-active polymer remained atoxic toward all the tested organisms.

Poly(dimethyl siloxane) (PDMS) network blends of amphiphilic acrylic copolymers with poly(ethylene glycol)-fluoroalkyl side chains for fouling-release coatings. II. Laboratory assays and field immersion trials

Amphiphilic copolymers containing different amounts of poly(ethylene glycol)-fluoroalkyl acrylate and polysiloxane methacrylate units were blended with a poly(dimethyl siloxane) (PDMS) matrix in different proportions to investigate the effect of both copolymer composition and loading on the biological performance of the coatings. Laboratory bioassays revealed optimal compositions for the release of sporelings of Ulva linza, and the settlement of cypris larvae of Balanus amphitrite. The best-performing coatings were subjected to field immersion tests. Experimental coatings containing copolymer showed significantly reduced levels of hard fouling compared to the control coatings (PDMS without copolymer), their performance being equivalent to a coating based on Intersleek 700™. XPS analysis showed that only small amounts of fluorine at the coating surface were sufficient for good antifouling/fouling-release properties. AFM analyses of coatings under immersion showed that the presence of a regular surface structure with nanosized domains correlated with biological performance.